Adjustable chair

ABSTRACT

A dental chair is equipped with a cushion roll between the backrest and the seat rest to provide a continuous supporting surface extending from the backrest to as far as the bottom of the leg rest. Single or dual controls are provided on the backrest, preferably along the opposite side edges of the backrest. Where dual controls are employed, a signal from a dental assistant&#39;&#39;s control will not operate the chair except in the absence of a signal from the dentist&#39;&#39;s control, which preferably overrides the assistant&#39;&#39;s control. A shroud connected to the seat rest is biased into engagement with the backrest adjacent the pivotal connection of the backrest and seat rest. Continuous return of the backrest to upright position may be effected by a holding device incorporated in the control unit, with provision for deactivation when a control switch for reclining the backrest is subsequently actuated. During movement of the backrest to various angular inclinations the arm rest is maintained in substantially parallel relation to the seat rest.

United States Patent 2,714,922 8/ l 955 McKibbon et a1.

Inventors Norris 0. Taylor Swarthmore, Pa.; Wilmer P. Uhler, Tottenville, Staten Island;

John M. Gardella, Staten Island, N.,Y.; Jim

C. Cahlik, Parma, Ohio Appl. No. 722,504 Filed Dec. 28, 1967 Division of Ser. No. 475,181, July 27, 1965, Pat. No. 3, 414,324 Patented May 11, 1971 Assignee Pennwalt Corporation ADJUSTABLE CHAIR 18 Claims, 41 Drawing Figs.

US. Cl 297/71 297/316, 297/391, 297/411, 297/330 Int. Cl ..A47c l/037, A47c l/04 Field of Search 297/68, 83, 84, 85, 86, 87, 88, 89, 90, 91, 330, 339, 347, 348, 316

References Cited UNITED STATES PATENTS 2,987,116 6/1961 Golden 297/330X 3,014,757 12/ 1961 Pilcher et a1. 297/85 3,016,264 l/l962 Hughes 297/ 69 3,025,108 3/1962 Teague.... 297/411X 3,173,720 3/1965 Noda 297/330X 3,191,990 6/1965 Rugg et a1. 297/83 3,330,595 7/ 1967 Svard 297/71 Primary ExaminerJames T. McCall Attorney-Mason, Porter, Diller and Brown ABSTRACT: A dental chair is equipped with a cushion roll between the backrest and the seat rest to provide a continuous supporting surface extending from the backrest to as far as the bottom of the leg rest. Single or dual controls are provided on the' backrest, preferably along the opposite side edges of the backrest. Where dual controls are employed, a signal from a dental assistants control will not operate the chair except in the absence of a signal from the dentists control, which preferably overrides the assistants control. A shroud connected to the seat rest is biased into engagement with the backrest adjacent the pivotal connection of the backrest and seat rest. Continuous return of the backrest to upright position may be effected by a holding device incorporated in the control unit, with provision for deactivation when a control switch for reclining the backrest is subsequently actuated. During movement of the backrest to various angular inclinations the arm rest is maintained in substantially parallel relation to the seat rest.

ATENTED m1 1 um I 34,578,379

INVENTORS NORRIS O. TAYLOR WILMER P. UHLER JOHN M. GARDELLA 8| JIM C. AHLIK ATTORNEY PAiem nuimian 3,578,379 .SHEET 020 1 t i 55 v 29' Connectors Limit Switch Tilt-Up Limit Switch Reciine Motot Back-Recline BiTiIt-Up Limit Switch C l Bose INVENTORS NORRIS O. TAYLOR I $16.4 ihi'l ii. RGAURHDLEELFLA 8i JIM C. AHLIK BY A ORNEY PATENTEDHAYHIH?! SHEET 03 0F INVENTORS PATENTEU m1 1 |97l SHEET 08 [1F WILMER E UHLER JOHN M. GARDELLA a JIM C. AHLIK A ORNEY pmE-msuumnan 3578-379 SHEET 10 0F 13 I6 J I 56 L O \"kzl.

2s NORRIS O. I A $558 WILMER P. UHLER JOHN M. GARDELLA 8 JIM C. CAHLIK A ORNEY PATENTEU m1 1 ml SHEET 11 [1F INVENTORS NORRIS o. TAYLOR WILMER e UHLER JOHN M. GARDELLA a mm c. CAHLIK BY ATT NEY PATENTEU MAYI 1 19m 3578379 sum 12 0F 1 INVENTORS NORRIS O. TAYLOR WILMER R UHLER JOHN M. GARDELLA 8 JIM C. CAHLIK ATTORNEY PATENTEU m1 1 19m 3578.379

INVENTORS NORRIS O. TAYLOR WILMER P UHLER JOHN M. GARDELLA 45o BY JIM (1 an arm rest wherein synchronous motions of various elements of the chair are designed such that a patient may be placed in the most convenient positions for the many and varied operations and allowing for the maximum functionability for a dentist or surgeon and yet retaining the dignity and comfort of the patient.

Another important object of the invention is the provision of an adjustable chair wherein a leg rest is pivotally mounted to a seat rest so as to provide a kneebreak therebetween, and the provision of automatic positioning of the leg rest relative to the seat rest to provide the most comfortable position for a patient when the backrest is in either its upright position or when in its reclined position.

Another object of this invention is to provide single control means for actuating the various motions of the adjustable chair.

Another object of this invention is to provide separate control means so that various synchronous motions of the chair elements may be actuated from the dentist's side" or from the assistant's side" of the chair.

Another object of the invention is to provide an override control means so that the dentists controls lock out the controls of the assistant-thus maintaining control by the dentist.

Another object of this invention is to provide a new and novel switch means which, upon actuation, causes the backrest to return from a reclined position to a fully upright position. v

A further object of this invention is to provide an adjustable chair wherein a backrest is pivotally mounted to a seat rest at a point above the plane of the seat rest so as to minimize rocking of an occupants clothes as the backrest is pivoted from an upright position to a reclined position relative to the seat rest.

A further object of this invention is to provide an adjustable chair wherein the backrest is pivotable from an upright position to a fully reclined position wherein the backrest is inclined below a horizontal position so as to aid in reviving a patient who has fainted, by increasing blood circulation to the patients head, or for placing a patient in position for some particular type of operation.

A further object of this invention is to provide a release mechanism for the arm rest whereby the arm rest is pivotally mounted on a portion of the backrest and is swingable away from the seat rest to provide for easy patient admittance and departure.

A further object of this invention is to provide a chair with a two-piece backrest portion thereby adapting the chair for use with interchangeable headrests.

Another object of this invention is to provide a shroud or cover plate which is pivotally mounted upon a rear portion of the seat rest so as to shield the actuating mechanism of the chair and prevent personal injuries.

A further object of this invention is to provide a novel transition roll which is located between the seat rest and the backrest thereby ensuring maximum patient comfort for all positions of the backrest relative to the seat rest.

A still further object of this invention is to provide an ad justable chair, of the type set forth above, wherein separate means are provided for adjusting the leg rest relative to the seat rest.

With the above and other objects in view that will hereinafter appear, the nature of the invention will be more clearly understood by reference to the following detailed description, the appended claimed subject matter and the several views illustrated in the accompanying drawings:

In the drawings:

FIG. 1 is a perspective view of an adjustable chair which is illustrative of the present invention.

FIG. 2 is a diagrammatic view and illustrates the major chair elements in an upright position and, in broken lines, in a partially reclined position.

FIG. 3 is a diagrammatic view, similar to FIG. 2, and illustrates the chair elements, in broken lines, in a more fully reclined position, and in full lines, illustrates the chair elements with the backrest thereof being in a fully reclined position so as to be inclined below the horizontal.

FIG. 4 is a schematic diagram illustrating the various electrical components incorporated in the adjustable chair.

FIG. 5 is a vertical sectional view, taken on line 5-5 of FIG. 1, and illustrates the mechanism for actuating the pivotal movements of the major chair elements.

FIG. 6 is a transverse sectional view, taken on line 6-6 of FIG. 5, and illustrates the seat rest and leg rest with portions broken away to show a portion of the thrust means for pivoting the leg rest and seat rest.

FIG. 7 is a vertical sectional view, taken on line 7-7 of FIG. 5 and illustrates a pair of supporting members fixedly secured to the seat rest and pivotally supporting the shroud member.

FIG. 8 is a vertical sectional view, taken along line 8-8 of FIG. 7 and illustrates a crosshead which is attached to the piston rod of a conventional lift mechanism, and also illustrates the pivotal mounting of the seat rest to the crosshead.

FIG. 9 is a vertical sectional view, taken on line 9-9 of FIG. 8, and illustrates a guide slot which is formed on the crosshead for cooperation with an extension of a link which is fixedly secured to the underside of the leg rest.

FIG. 10 is a sectional view, taken on line 10-10 of FIG. 5, and illustrates the mounting of a roller on the forward end of the thrust bar mechanism.

FIG. 11 is a vertical transverse sectional view, taken on line 11-11 of FIG. 5, and shows the arrangement of drive sprockets and idler sprockets for connecting the actuating motor to the operating mechanisms.

FIG. 12 is a vertical sectional view, taken on line 12-12 of FIG. 11, and shows, in elevation, the arrangement of one of a pair of operating screws mounted for rotation on the underside of the seat rest.

FIG. 13 is a sectional view, taken on line 13-13 of FIG. 12, and illustrates a guide arrangement for guiding the movement of a channel-shaped thrust bar.

FIG. 14 is a sectional view, taken on line 14-14 of FIG. 12, and illustrates a manner in which a nut member on the screw is pivotally secured to a forward portion of a yoke member.

FIG. 15 is a sectional view, with parts broken away for clarity, and illustrates the position of the seat rest and leg rest when the backrest is in its substantially upright position.

FIG. 16 is a sectional view, similar to FIG. 15, and illustrates the position of the seat rest and leg rest with the backrest in a reclined position.

FIG. 17 is a partial plan view showing the arm rest being pivotally mounted to a portion of the backrest and being pivotally mounted therewith relative to the seat rest.

FIG. 18 is a sectional view, taken on line 18-18 of FIG. 17, and illustrates the manner in which the arm rest is pivotally mounted upon a forwardly extending flange portion of the backrest, and also showing the pivotal mountings for connecting the backrest and shroud to upstanding support members on the seat rest.

FIG. 19 is a rear elevational view, with portions broken away for clarity, and illustrates a set of control switches being mounted at each side of the backrest.

FIG. 20 is a vertical sectional view, taken on line 20-20 of FIG. 19 and illustrates the manner in which an adjustably positionable headrest is mounted upon the backrest.

FIG. 21 is a fragmentary perspective view of the backrest and the headrest, with the headrest in a partially assembled position relative to the backrest.

FIG. 22 is a fragmentary perspective view of the switches and mounting plate which are located on the dentists side of the backrest.

FIG. 23 is a partially exploded view of the switches which are located on the dentist's side of the chair.

FIG. 24 is an elevational view of the assembled switches which are illustrated in FIG. 23.

FIG. 25 is an enlarged sectional view, taken on line 25-25 of FIG. 24, and shows a novel spring member which is mounted between the.recline switch and the tiltup switch on the dentists side of the backrest.

FIG. 26 is a fragmentary view illustrating the tiltup" switch in a fully depressed and locked position, and illustrates the recline switch in a released position, and also shows the novel spring member in a bowed position which results from engagement of the spring member by a cam located upon the tiltup" switch.

FIG. 27 is a view similar to FIG. 25 and illustrates the cam on the tiltup" switch engaged with the spring member for causing distortion thereof.

FIG. 28 is a cross-sectional view of the pushbutton portion of the recline switch.

FIG. 29 is a cross-sectional view of the pushbutton portion of the tiltup switch.

FIG. 30 is a fragmentary perspective view of the switches and mounting plate located on the assistants side of the backrest.

FIG. 31 is a sectional view of the assistants control and shows a portion of the wiring therefor.

FIG. 32 is a fragmentary perspective view of a modified form of a backrest wherein an upper portion of the backrest is removable from a lower portion thereof to provide for interchangeability of head rests.

FIG. 33 is a front elevational diagrammatic view of the twopiece backrest, with portions broken away for clarity, and illustrates the adjusting mechanism for adjustably positioning the upper portion of the two piece backrest relative to the lower portion thereof.

FIG. 34' is a vertical section, taken on line 3 l-34 of FIG. 33, and illustrates a support rod fixedly secured to the top portion of the backrest and slidably received'within a guide slot in the lower portion of the backrest.

FIG. 35 is a sectional view, taken on line 35-35 of FIG. 33, and illustrates the control means for effecting adjustment of the support rod within the lower portion of the backrest.

FIG. 36 is a plan view of a modified form of seat rest and leg rest wherein an adjusting mechanism is provided for selectively adjusting the leg rest relative to the seat rest.

FIG. 37 is a fragmentary elevational view, of FIG. 36, and illustrates the manner in which a pair of channels can be adjusted inlength to provide for adjusting the leg rest relative to the seat rest.

FIG. 38 is a plan view of another modification of thc invention wherein the leg rest and seat rest are provided with an adjusting mechanism for varying the inclination of the leg rest relative to the seat rest.

FIG. 39 is a fragmentary elevational view of FIG. 38 and illustrates the pivotal mounting forone of a pair of plate mem bers on the top side of the leg rest.

FIG. 40 is a view of the underside of a leg rest and seat rest wherein a further modification of the invention includes a separate motor mounted on the underside of the leg rest and cooperating with a crank for varying the inclination of the leg rest relative to the seat rest.

FIG. 41 is a fragmentary elevational view and illustrates the manner in which the motor and crank are connected between the seat rest and the leg rest.

Referring to the drawings in detail, there is illustrated in FIG. 1 a new and novel adjustable chair, generally indicated by the numeral 10, which chair is particularly adapted for use in the practice of dentistry. The chair It) includes a conven tional lift-mechanism II,- which may be actuated by a conventional foot-operated switch 12 for vertically raising and lowering the chair 10.

A forwardmost portion of the chair It) comprises a leg rest portion 13 which depends forwardly and downwardly from a seat rest portion 14. The leg rest portion 13 and seat rest porswitch tion 14 includes a cushion member 15 which extends, without interruption, from a rearward portion of the seat rest portion 14 to a lower portion of the leg rest portion '13 so as to provide a continuous uninterrupted supporting surface.

A backrest portion 16 is pivotally mounted, at 18, to an upstanding portion of the seat rest portion 14, and has a pair of arm rests 20 pivotally connected thereto, at 22. The backrest portion 16 has a headrest 24 adjustably mounted thereon by a strap member 25. The transition roll 26 is located at the juncture between the seat rest portion 14 and the backrest portion 16 so as to provide a continuous supporting surface between the seat rest portion 14 and the backrest portion 16 regardless of any changes in the relative position of the backrest portion 16 and the seat rest portion 14.

Control means 28 are located on a side of the backrest portion 16 and include a rocker switch 29 for vertically raising and lowering the chair It], a pushbutton 30 for moving the backrest portion 16 to a reclined position, and a second pushbutton switch 31 for moving the backrest portion 16 to an upright position. The rocker switch 29 actuates the lift mechanism Ill in the same manner as the foot-operated switch 12 so that the chair 10 may be adjusted by the switch which is most conveniently located for the dentist during any given operation. As will be more fully described, a dual set of control means is located on the other side of the backrest portion I6 so that the dentists assistant is also provided with convenient control for varying the positions of the chair 10.

FIGS. 2 and 3 are diagrammatic illustrations of the major elements of the chair It). The full line position of FIG. 2 illustrates a leg rest 34 pivotally mounted to a bracket 35 which is fixedly secured to a seat rest 36. The seat rest 36 has a pair of supporting members 37 fixedly attached thereto along lateral edges at the rearmost portion thereof, and a backrest 38 includes a pair of forwardly extending flange portions which are pivotally connected to the support members 37, at 40, above the plane of the seat rest 36.

Actuating means, generally indicated by the numeral 45, are provided for adjustably positioning the various elements of the chair It). It will be apparent from a comparison of the fullline positions and the broken-line positions of FIGS. 2 and 3, that the actuating mechanism 45 causes the backrest 38 to be movable from the upright position of FIG. 2 through a series of intermediate positions to a completely reclined position wherein the backrest 38 is inclined at an angle of approximately 8 below the horizontal, as is shown in the full line position of FIG. 3. j

A general understanding of the operation of the chair It] will become apparent by consideration of the wiring diagram illustrated in FIG. 4. A power supply, generally indicated by the numeral 50, is connected to a terminal board 51 to provide power for operating the various mechanisms. The conventional lifting mechanism 11 is actuated by a motor 52 which is controlled by the foot-operated switch mechanisms 12 and 12, located at the base of the chair 10, or by the control means 28 and 28' which are located along opposite sides of the backrest portion 16. Movement of the switch 12 from its normally opened position to the closed position will actuate the motor 52 and thus causing the chair 10 to raise. In order to lower the chair 10, it is necessary to actuate the switch 12' so as to open an oil-release solenoid valve thus permitting the chair It) to lower.

The second point at which the chair 10 can be raised or lowered is at either of the control panels 28 or 28'. The rocker switches 29 and 29"are conventional three-position switches which are normally open. When the upper portion of either rocker switch 29 or 29' is pressed, the motor 52 starts and causes the chair 10 to raise. Pressing the lower portion of either of the rocker switches 29 or 29' causes a conventional solenoid valve to open which releases the oil pressure in the lift mechanism I I, thus permitting the chair 10 to lower. If by accident, the foot lever 12 and either of rocker switches 29 and 29' are actuated for opposing motions, no harm will come to the chair 10 although this is not recommended.

The reclining and tilting up operation of the chair is controlled by pushbutton switches 55 and 55', and 56 and 56', respectively. Switches 55 and 56 are located at the control panel 28 on the dentists side of the chair 10, while the switches 55 and 56' are located at the control panel 28 on the assistant's side of the chair. The chair 10 can be brought to any angle of recline by simply pressing the correct switch for the desired motion. Pressing the switch 55 or 55' would recline the chair 10 and, by releasing the finger pressure from the switch, thechair motion will stop at any angle desired. Switches 55 and 56' will tilt the chair 10, i.e. the backrest 38, up from the horizontal position. This operation can be accomplished by either pressing the switch 56 or 56', and holding it, or the switch 56 can be pushed in and then pushed clockwise to a lock and hold position. The switch will hold in this position throughout the travel of the chair and return to its normal position when the recline" switch 55 is actuated. This feature of the invention will be more clearly defined with the explanation of FIGS. 24-27,

An important feature of this invention is that means are provided whereby the dentists controls will override any command given by the assistant's controls. From a consideration of FIG. 4, it will be apparent that power is fed to the assistants switches 55' and 56' through the wire 60 and connector 61. Tracing the wire 60 through the dentist's switches 56 and 55 will show a complete circuit so that actuation of either of the assistant's switches 55 or 56 will cause the respective desired motion of the chair. However, if the dentist presses either switch 55 to cause the chair to recline, or pushes the switch 56 to cause the chair to tilt up, the circuit to the assistants switches 55' and 56', through wire 60 and connector 61 is broken so that no conflicting signals can be given to the assistants switches.

The reclining mechanism for the chair 10 is operated by motor 62 which is preferably a single phase AC reversible motor. A limit switch 63 is provided for shutting off motor 62 when the chair has reached its upright" position, and a similar limit switch 64 is provided for shutting off motor 62 when the chair has reached its extreme recline position.

As is shown in FIGS. 5--8 a plunger or piston rod 70 extends upwardly from the chair base 11 and is part of a conventional mechanism for raising and lowering the chair 10. A horizontally disposed crosshead 71 is bolted or otherwise secured to the plunger '70 so as to be maintained in a substantially horizontal position. A pivot rod 72, see FIG. 8, is carried by crosshead 71 and is transversely aligned at the rearmost portion of the crosshead 71. A pair of pivot blocks 73 are pivotally mounted upon the rod 72 at the lateral edges of the crosshead 71. A plurality of screws 74 are provided for fixedly securing the seat rest 36 to pivot blocks 73 (See FIGS. 7 and 8) such that the seat rest 36 is mounted on the pivot rod 72 for pivotal motion relative to the crosshead 71 and plunger or piston rod 70.

As is best shown in FIGS. 5, and 16, a pair of upstanding support plate members 37 are fixedly secured to the rearwardmost lateral edge portions of the seat rest 36. The backrest 38 is provided with a pair of lateral flange portions 39 which extend forwardly from a lowermost portion thereof. Flange portions 39 are each pivotally secured to a respective one of the pair of support plate members 37 so that the backrest 3.8 is mounted for pivotal motion, at 40, between an upper position to a fully reclined position wherein, as is shown in FIG. 3, the backrest 38 is positionable at approximately 8 below the horizontal.

The chair 10 is operated between the recline and upright positions by the motor 62. The motor 62 is provided with support bracket means 80 (See FIG. 6) which is fixedly secured to a front underside portion of the seat rest 36 by a plurality of bolts 82. As is clearly shown in FIGS. 6, 11 and 12, a forward support bracket 85 is secured to and extends transversely of a front portion of the seat rest 36, and cooperates with a rearward support bracket 86, for supporting a pair of parallel screws 87 and 88 beneath lateral edges of the seat rest 36. As

shown in FIG. 12, a beveled washer is mounted on each of the elements 87 and 88 between the bracket 85 and the collar 89. A drive sprocket 90 is mounted upon the forward support bracket 85 and is driven by the motor 62 through a gear reducer 91. A drive chain 92 partially'encircles the drive sprocket 90 and extends about a driven sprocket 94, which is secured to drive screw 87, and also extends about driven sprocket 95 which is secured to drive screw 88. A pair of idler sprockets 96 and 97 are mounted for rotation on bracket 85, and it is preferable that the idler sprocket 96 be adjustably mounted upon the bracket 85 so as to provide a means for increasing or decreasing tension in the drive chain 92.

Each of the screws 87 and 88 is provided, respectively with a ball nut 98 and 99 which are mounted for translation thereon. As is best shown in FIGS. 12 and 14, the ball nut 98 is provided with a post 100 which is disposed thereabove for cooperating with limit switch 63 to stop the motor 62 when the backrest 38 reaches its fully upright position, and also cooperates with limit switch 64 for stopping motor 62 when the backrest 38 reaches its fully reclined position.

A generally U-shaped yoke member 102 is provided at each of its forwardly extending leg members with a bifurcated bracket 103 and 104 for pivotally connecting the yoke member 102 to a respective one of the ball nuts 98 and 99, in the manner best illustrated in FIGS. 6 and 14. As is clearly shown in FIGS. 5 and 6, a pair of brackets 108 are fixedly secured to a central lowermost portion of the backrest 38 and are pivotally connected to the bight portion of the U-shaped yoke member by a pivot pin 110. Upon actuation of either of the pushbutton switches 56 and 56', the motor 62 drives through gear reducer 91 to rotate the screws 87 and 88 thus causing ball nuts 98 and 99 to move forwardly beneath the seat rest 36 and exerts a force upon brackets 108 so as to pivot the backrest 38 toward a reclined position about the pivot 40.

Each side of the yoke member 102 is provided with a depending boss and 122. A pair of thrust bars 124 and 126 are pivotally connected to the bosses 120 and 122 by pivot means 128 and 130 respectively. Thrust bars 124 and 126 extend forwardly along lateral edges portions beneath the seat rest 36 and, as is best shown in FIGS. 2, 6, l2 and 13, the thrust bars are guidingly mounted upon roller members 132 and 134, which are in turn supported by depending brackets 35. The forwardmost end portions of the thrust bars 124 and 126 have rotatably mounted thereon a pair of roller members and 142, respectively, which are guided for movement along the underside of the seat rest 36 by suitable U-shaped guide members 144, as is best shown in FIGS. 5 and 10.

As is best shown in FIGS. 6 and 15, a pair of links 146 and 148 are fixedly secured to uppermost lateral portionsof the leg rest 34 and are pivotally connected on pivot pins 150 which are carried by the brackets 35 which depend from the seat rest 36. Links 146 and 148 have rearwardly extending legs 152 and 154, respectively, and carry roller members 156 and 158. As is clearly shown in FIGS. 5-8, a pair of guide plates 160 and 161 are fixedly secured by suitable screws 162 to the underside of crosshead 71 to provide guide slots 164 for receiving therein the roller members 156 and 158. Such an arrangement provides for a lost motion connection between respective roller member 156 and 158 with the crosshead 71.

Actuation of either of the pushbutton switches 55 or 55' causes the motor 62 to rotate the parallel screws 87and 88 such that the ball nuts 98 and 99 are moved forwardly thereon and causes the yoke member 102 to rotate the back rest 38 about the pivot 40. As the yoke member 102 moves downwardly and forwardly, the thrust bars 124 and 126 are driven forwardly to cause the leg rest 34 to move upwardly. The roller members 156 and 158 are restrained within the guide slots 164 and vertical movement is procluded. Consequently, the links 146 and 148 rotate upwardly about the axis of roller members 156 and 158 to cause upward movement of the pivot pin 150 and brackets 35. As a result, seat rest 36 is pivoted upwardly about the axis of pivot rod 72.

As a result 'of the foregoing operation, the chair is moved from an upright position toward the reclined position. Continued actuation of the switches 55 or 55' will cause the backrest 38 to assume the fully reclined position which is best illustrated by the full line position of FIG. 3. When the backrest 38 reaches the fully reclined position, the ball nut 98 actuates the limit switch 63 to deactivate the motor 62, and movement of the chair 10 ceases. Actuation of either of the switches 56 or 56 reverses the operation of motor 62 such that the backrest 38,. the leg rest'34 and the seat rest 36 are rotated from the reclined position toward the upright position.

It is desireable that the arm rest be moved in synchronism with the seat rest 36 and backrest 38. As is clearly shown in FIGS. 2, 17 and 18, each of the arm rests 20 is pivotally mounted at 170, on a respective one of the lateral flange portions 39 which are integral with the backrest 38. As is best shown in FIG. 18, the sleeve 172 is fixedly secured, such as by welds 174, to a respective flange portion 39. The pivot shaft 176 is mounted for rotation within the sleeve 172 and carried therewith as the backrest 38 rotates about the pivot 40. It is desirable that the arm rest20 be maintained in substantially parallel relation to the seat rest 36, as the seat rest 36 rotates about pivot rod 72. Therefore, a crank arm 178 is mounted upon the pivot shaft 176 for rotation therewith. An arm link 180 has one end thereof pivotally connected to the crank arm 178, at 182, and the other end of the arm link 180 is pivotally connected, at 184, to the support member 37 which extends upwardly from the seat rest 36. As the backrest 38 pivots relative to the seat rest 36, the pivot shaft 176 is carried with the backrest 38 but rotates within the sleeve 172 such that the arm rest 20 is maintained in substantially parallel relation to the seat rest 36.

In order to provide for easy admittance and departure from the chair 10, it is desirable that the arm rests 20 be adapted to swing up and out of the way. As is shown in FIGS. 17 and 18, the pivot shaft 176 is provided with a substantially radially disposed opening 190 for receiving a locking member or pin 192 therein. A bushing 194 is fixedly mounted within the arm rest 20 and provides for sliding motion of the pin 182 therein. A release lever 196 is pivotally mounted to the arm rest 20, at 198, and is connected to the locking member or pin 192 by a link 288. The rearward portion of the release lever 196 is disposed in an accessible position at the rear of arm rests 20 such that upward motion of the release lever 196 will raise the locking member or pin 192 from within the opening 190 and thus permit arm rests 20 to freely rotate about the pivot shaft 176.

In order to assure that pin 192 seats within the opening 190, a spring 202 has one end attached to the release lever 1% and the other end is connected to a stud 204 which is provided on the arm rests 20. Thus, the release lever 196 is continually biased in a counterclockwise direction about the pivot 198, as is shown in FIG. 17, such that the locking member or pin 192 is seated within opening 190.

The transition roll 26 is best illustrated in FIGS. 1 and 5. The transition roll 26 is a separate, pillowlike member which is formed of resilient deformable material, such as foam rubber or the like. The transition roll 26 is placed between the backrest 38 and the seat rest 36, and is held in position by a support bracket 210, as is shown in FIG. 5, and by frictional engagement with the seat rest portion 14 and the backrest portion 16. As the backrest 38 pivots to a reclined position, the transition roll 26'is squeezed between the seat rest portion 14 and the backrest portion 16 so as to provide a comfortable cushion-piece to support the occupants lower back portion. The transition roll 26 is unique in that no gap exists between the lowermost portion of the backrest portion 16 and the rearwardmost portion of the seat rest portion 14 at any time during movement of the chair It) toa reclined or upright position.

In modern professional practice, it is becoming more conventional for the dentist to be in a seated position during operation upon a patient. As a result, the dentist's knees are located closely adjacent to the lower rear portion of the chair 10. In order to avoid interference with the yoke member 102, and to preclude possible injury to the dentist, it is a feature of this invention to provide a cover plate or shroud 215 to provide an absolutely clear backrest free from all protrusions, thus eliminating any knee interference. As is shown in FIGS. 1, 17 and 18, the shroud 215 is provided with a pivot stud 216 and is pivotally mounted upon the upstanding support members 37 at opposite sides of the rear of the seat portion 36. As is shown in FIG. 16, a hook 220 is provided on the shroud 215, and a spring 222 connects the hook 220 to a chair frame extension such that the shroud 215 is biased upwardly toward engagement with the backrest 38.

As is shown in FIG. 19, the control means 28 and 28 are mounted on opposite side edges of the backrest portion 16. As

7 was pointed out above, in connection with FIG. 4, the dentists controls 28 override commands initiated at the assistants controls 28 so that the dentist retains final control for moving the chair between the upright and reclined positions.

FIGS. 20 and 21 illustrate the manner in which the head rest 24 is adjustably mounted on the backrest portion 16. The strap 25 is fixedly secured to a rear portion of the headrest 24, and is provided with a weight 25. The weight 25' and a portion of the strap 25 are insertable within an opening 230 which is located in the top portion 232 of the backrest portion 16. Headrest 24 is preferably provided with a storage compartment 234 for storing a roll of sanitary paper 236, and the paper 236 can be entrained over the top of the headrest 24 and be fastened at the bottom of the headrest 24 by a combined holding-and-cutting strap 238.

The dentists controls 28 are illustrated in FIGS. 2229. The rocker switch 29, and the pushbutton switches 55 and 56 are mounted upon a support bracket 250 which is fixedly secured to the dentists side of the backrest portion 16 by an exterior cover plate 252 and a pair of suitable screws 254.

A feature of this invention is the provision of a leaf spring 260 which extends between the switches 45 and 56. A stop lug 262 is centrally mounted upon the bracket 250 intermediate the switches 29 and 55. The spring 260 includes a pair of ears 264 mounted in a pair of slots in the stop lug 262. The opposite end of spring 261) is provided with a pair of extension arms 266 and 268 which extend on opposite side portions of a reduced portion 270 of the switch 56. A cam 272 is fixedly secured to the reduced portion 270 and is disposed for engagement with the free edge of extension arm 268.

After the dentist has completed his work upon a patient, the

pushbutton switch 56 is depressed in order to raise the backrest 38 from a reclined toward a upright position. In order to avoid holding the switch 56 depressed during the time that the mechanism raises the chair to its full extent of travel, a lock pin 274, as is best shown in FIG. 26, is fixed in casing 273 and cooperates with a slot 275 which is provided in barrel member 276. Barrel member 276 is lightly biased outwardly to the left, as is shown in FIG. 26, by a spring, now shown. The finger-engaging portion of the switch 56 is provided with a reduced section to provide a grip 278. A knurled fitment 279 is provided with a bead 280 and frictionally connects the grip portion 278 to the barrel 276 for movement therewith. As the switch 56 is depressed, lock pin 274 rides in slot 275 and, upon slightrotation of the grip portion 278 and barrel member 276 in a counterclockwise direction, as viewed in FIGS. 25 and 27, a shoulder 280 is positioned for engagement with the lock pin 274 when the pressure on the switch 56 is released and the switch 56 is biased outwardly by the spring, not shown. During rotation of the grip portion 278 and barrel 276, the cam 272 engages the free edge portion of the extension arm 268 and distorts the leaf spring 260 from the position shown in FIGS. 24 and 25 to the position shown in FIGS. 26 and 27. The portion of the spring 260 near the ears 264 is precluded from movement by the stop lug 262 such that the spring 268 becomes pronouncely bowed and moved toward contact with the finger-engaging portion of the switch 55. The switch 56 remains in active position and the chair 10 moves from a reclined position to a fully upright position whereupon ball nut 100 on the screw 87 actuates the limit switch 64 so as to turn off the'motor 62. At the start of the next operation,

after the patient is seated, the switch 55 is depressed, so as to move the chair 10 toward a reclined position, and the bowed portion of spring 260 is flattened and causes the extension arm 268 to rotate the switch 56 through engagement with the cam 272, and cause shoulder 280 to become disengaged with the lock pin 274. As a result, the switch 56 is forced outwardly, by its biasing spring, to its inactive position. Switch 55 may also be provided with a lock pin 282 and a slot 283, if so desired.

FIGS. 30 and 31 illustrate the controls 28-for the assistants side of the chair 10. Roder switch 29' is actuated to raise and lower the chair 10, pushbutton switch 55 is actuated to move the chair 10 to a reclined position, and pushbutton switch 56 is pushed to raise the chair 10 to its upright position. As previously pointed out, switches 55' and 56 can operate the chair 10 only in the absence of an overriding signal from the dentist's switches 55 and 56.

FIGS. 32-35 illustrate a modified version of a chair, generally indicated by the numeral 300, which includes a twopiece backrest comprising a lower portion 304 and a separable top portion The top portion 306 is adapted to be equipped with the adjustably mounted headrest 24 in the same manner as was described in connection with the FIGS. and 21.

'Ine separable top portion 306 is provided with a support rod 303 .which is fixedly secured thereto on brackets 310. A pair of channel members 312 and 314 are fixedly secured to a back portion 316, and cooperate with the plate member 318 to provide a guide slot 320 which is adapted to receive the support rod 308 therein. A stop member 322 is pivotally mounted upon the channel member 314 by a pivot pin 324 so that a portion of the stop member 322 extends into the slot 320 and is adapted to engage support rod 308 and hold the same inv a vertically adjusted position. The stop member 322 carries a strike plate 326 which is connected to a biasing spring 328 mounted upon a hook member 330 which is fixed to one of the bracket member 314. Strike plate 326 is disposed for engagement by a spring-loaded plunger 332 which is mounted on an upright side of the lower portion 304. The upper portion 306 can be adjusted relative to the lower portion 304 by depressing the plunger 332 and moving the upper portion 306 to the desired vertical position, and releasing plunger 332 so that spring 328 biases the stop member 322 into holding engagement with the support rod 308. From the foregoing, it will be apparent that the chair 300 is adapted for use with the upper portion 306 and headrest 24, and the chair 300 is also adaptable for use with previously known types of traditional headrests. More important, should a future design of a headrest be introduced into the profession, the removable top portion 306 can be changed without changing the entire back.

Another feature of the chair 300 is that the backrest portion 306 may be removed, and the strap of headrest 24 may be insertedinto theguide slot 320 so as to place the headrest 24 upon the lower portion 304 and thus adapt the chair 300 for use with children instead of adults.

FIGS. 36 and 37 illustrate a modification of the invention wherein a pair of laterally disposed thrust bars 400 each include an inner U-shaped channel member 402 which is nested within an outer U-shaped channel member 404. Each of the channel members 404 is provided with a rotatably mounted roller 406 for cooperation with the leg rest 34. Channel members 402 and 404 are each provided with adjustment holes 408 and 410, respectively. Suitable lock pins, or spring-loaded catch members, not shown, are provided for placement within aligned pairs of holes 408 and 410 for adjustably positioning the channel member 404 with respect to the channel member 402. As is apparent from a consideration of FIG. 37, movement of the roller 406 from the full-line position to the dotted line position, prior to actuation of the chair recliningmechanism, results in deactivating the thrust bars and prevents upward motion of the leg rest 34 and seat rest 36.

Conversely, if it is desired to separately adjust the leg rest 34 and seat rest 36, relative to the backrest 38, channel members 402 and 406 may be unlocked from each other and channel member 404 may be extended to the right, as viewed in FIG. 37, thus causing the leg rest 34 and seat rest 36 to pivot up wardly.

Another modifiedform of the invention is illustrated in FIGS. 38 and 39. A pair of cover plates 420 are pivotally mounted to the leg rest 34 by a pair of pivot pins 422 carried by mounting brackets 424 and overlie openings 426. With the cover plates 420 free to pivot about the pivot pins 422, actuation of the chair reclining mechanism causes the thrust bars 124 and 126 to raise the, cover plates 420 without any corresponding movement of the leg rests 34 and seat rest 36. Accordingly, only the leg rest portion of cushion member 15 is raised and no movement of the seat rest portion of the cushion member 15 occurs.

Another modification of the invention is illustrated in FIGS. 40 and 41. In this form of the invention, a separate motor and gear-reducer 450 is mounted on the underside of the leg rest 34 and includes a connector 452 fixedly connected to a drive shaft 454. A pair of crank arms 456 are secured to the drive shaft 454 for rotation therewith. A thrust bar 458 is pivotally secured, at 460 to a bracket 462 which is fixedly secured to the underside of. the leg rest 34. Thrust bar 458 is also pivotally connected to the crank arms 456 by a pivot pin 464. When motor 450 is operated, rotation of drive shaft 454 and crankarms 456 causes the leg rest 34 to pivot upwardly relative to pivot pin 464. If it is desirable only to change the position of the leg rest 34, it is necessary to remove plates from the crosshead 71 so that the extension 152 of bracket 148 is free to pivot relative to the crosshead 71. As a result, the motor 450 will cause the leg rest 34 to rotate about pivot 150. If plates 160 are not removed, it should be noted that motor 450 is capable of causing the chair 10 to be adjusted toward a reclined or upright position. In such a case, motor 450 will cause the leg rest 34 to pivot upwardly about the roller 156, thus causing the seat rest 36 and backrest 38 to move toward and away from the positions illustrated in FIGS. 15 and 16.

In each of the various embodiments of the invention, it is desirable that the various linkages operate smoothly so as not to cause patient apprehension. Accordingly, counterweight 480 is preferably mounted upon the leg rest 34 beneath the leg rest portion of cushion member 15, as is best shown in FIGS. 5 and 6. The counterweight 480 compensates for any looseness in the operating mechanisms and also assists the motor 62 during the time that the chair 10 is being raised to its upright position.

While preferred forms and arrangements of parts have been shown in illustrating the invention, it is to be clearly understood that various changes in details and arrangements of parts may be made without departing from the spirit and scope of the invention, as defined in the appended claimed subject matter.

We claim:

1. A chair including a seat rest and a backrest, means pivotally connecting said backrest to said seat rest, means for causing said backrest to pivot relative to said seat rest, and a transition roll disposed between said seat rest and said backrest so as to provide a continuous supporting surface between said backrest and said seat rest in all relative positions of said backrest and said seat rest, said transition roll being constructed of resilient material so as to be deformable during pivoting motion of said backrest relative to said seat rest.

2. A chair including a seat rest and a backrest, means for pivotally connecting said backrest to said seat rest, and a shroud, means pivotally connecting said shroud to said seat rest, and resilient means connected between said seat rest and said shroud for biasing an upper portion of said shroud into engagement with said backrest.

3. A chair including a backrest and a seat rest, means pivotally connecting said seat rest to said backrest, a motor, a control for saidmo'tor on the side edge'of said backrest, a driving connection between said motor and said backrest whereby operation of said motor causes pivoting of said backrest relative to said seat rest, an arm rest, means pivotally mounting said arm rest to said backrest, and means connecting said arm rest to said seat rest for maintaining said arm rest substantially parallel to saidseat rest in all positions of said backrest relative to said seat rest.

4. ln an adjustable chair of the type including a seat rest and a backrest pivotally mounted for movement relative to said seat rest, and motor means for actuating the pivotal movement thereof; said motor means comprising a reversible motor, and a set of control means located on a side edge of said backrest for reclining said backrest relative to said seat rest and for moving said backrest to an upright position relative to said seat rest. 4

5. in an adjustable chair as defined in claim 4 wherein a second set of control means is provided for reclining said backrest relative to said seat rest and for moving said backrest to an upright position relative to said seat rest, and means connecting said set of control means to said second set of control means for locking out said second set of control means whereby conflicting signals cannot be transmitted to said motor means.

6. In an adjustable chair as defined in claim 5 wherein said second set of controls is located on another side edge of said backrest.

7. in an adjustable chair as defined in claim 4 wherein said set of control means includes a three-position switch for moving said backrest to a reclined position and to an upright position relative to said seat rest; said three-position switch including first means for providing a neutral position, second means for actuating said motor means to recline said backrest rela tive to said seat rest, and third means for actuating said motor means for moving said back rest to an upright position relative to said seat rest.

8. In an adjustable chair as defined in claim 7 wherein said third means includes means for holding said switch in position to continually actuate said motor means until said backrest reaches the extreme upright position relative to said seat rest.

9. In an adjustable chair of the type including a seat rest and a backrest, support means fixedly secured adjacent to a lateral edge of said seat rest and extending upwardly therefrom in a first substantially vertical plane, said backrest including lateral flange portions each integral with a lowerportion of said backrest and extending forwardly therefrom in a second substantially vertical plane parallel to said first substantially vertical plane, and pivot means connecting said flange portions to said support means for pivotally mounting said backrest to said seat rest for rotation about a horizontal axis of said pivot means disposed above the plane of said seat rest.

10. In an adjustable chair as defined in claim 9 wherein means are provided for rotating said backrest to a lowermost position with said backrest being disposed below a horizontal plane passing through a portion of said backrest adjacent to said seat rest'.

11. In a dental chair having a seat rest and a backrest mounted for movement relative to said seat rest, a leg rest, means pivotally connecting said leg rest to said seat rest, a motor for actuating the pivotal movement of said leg rest, control means located on a side-edge of said backrest for controlling said motor to effect pivotal movement of said leg rest, and cushion means disposed over said seat rest and leg rest and extending without interruption from a rearward portion of said seat rest to a lower portion of said leg rest for providing a continuous uninterrupted supporting surface for all positions of said seat rest and said leg rest relative to each other.

12. An adjustable chair as defined in claim 4 wherein a second set of control means is provided for reclining said backrest relative to said seat rest and for moving said backrest to an upright position relative to said seat rest, said sets of control means being respectively located on opposite side edges of said backrest.

13. An adjustable chair of the type including a seat rest and a backrest pivotally mounted for movement relative to said seat rest, and motor means for actuating the pivotal movement thereof; said motor means comprising a reversible motor, and a set of control means located on said backrest for reclining said backrest relative to said seat rest and for moving said backrest to an upright position relative to said seat rest, wherein a second set of control means is provided for reclining said backrest relative tosaid seat rest and for moving said backrest to an upright position relative to said seat rest, and wherein one of said sets of control means is operable for reclining or moving said backrest in the absence of a signal from the other of said sets of control means.

14. An adjustable chair as defined in claim 6 wherein the second set of control means is operable in the absence of a signal from the other set of control means, and wherein a signal from the other set of control means overrides a signal from the second set of control means.

15. An adjustable chair as defined in claim 13 wherein said second set of control means is inoperable upon actuation of said other set of control means.

16. In an adjustable chair as defined in claim 4, further including means for elevating and lowering said chair, wherein said set of control means includes a three-position switch for raising said chair to an elevated position and for lowering said chair to a lower level position; said three-position switch including first means for providing a neutral position, second means for actuating said elevating and lowering means to raise said chair to an elevated position, and thirdmeans for actuating said elevating and lowering means for lowering said chair from an elevated position to a lower position.

117. An adjustable chair of the type including a seat rest and a backrest pivotally mounted for movement relative to said seat rest, and motor means for actuating the pivotal movement thereof; said motor means comprising a reversible motor, and a set of control means located on said backrest for reclining said backrest relative to said seat rest and for moving said backrest to an upright position relative to said seat rest, wherein said control means includes a switch for controlling movement of said backrest toward an upright position by energizing said motor means, and further including means for holding said switch in'position to energize said motor means until said backrest reaches an extreme upright position relative to said seat rest.

18. An adjustable chair as defined in claim 17 wherein said control means includes a second switch for controlling reclining movement of said backrest, and resetting means for deactivating said holding means incident to actuation of said second switch. 

1. A chair including a seat rest and a backrest, means pivotally connecting said backrest to said seat rest, means for causing said backrest to pivot relative to said seat rest, and a transition roll disposed between said seat rest and said backrest so as to provide a continuous supporting surface between said backrest and said seat rest in All relative positions of said backrest and said seat rest, said transition roll being constructed of resilient material so as to be deformable during pivoting motion of said backrest relative to said seat rest.
 2. A chair including a seat rest and a backrest, means for pivotally connecting said backrest to said seat rest, and a shroud, means pivotally connecting said shroud to said seat rest, and resilient means connected between said seat rest and said shroud for biasing an upper portion of said shroud into engagement with said backrest.
 3. A chair including a backrest and a seat rest, means pivotally connecting said seat rest to said backrest, a motor, a control for said motor on the side edge of said backrest, a driving connection between said motor and said backrest whereby operation of said motor causes pivoting of said backrest relative to said seat rest, an arm rest, means pivotally mounting said arm rest to said backrest, and means connecting said arm rest to said seat rest for maintaining said arm rest substantially parallel to said seat rest in all positions of said backrest relative to said seat rest.
 4. In an adjustable chair of the type including a seat rest and a backrest pivotally mounted for movement relative to said seat rest, and motor means for actuating the pivotal movement thereof; said motor means comprising a reversible motor, and a set of control means located on a side edge of said backrest for reclining said backrest relative to said seat rest and for moving said backrest to an upright position relative to said seat rest.
 5. In an adjustable chair as defined in claim 4 wherein a second set of control means is provided for reclining said backrest relative to said seat rest and for moving said backrest to an upright position relative to said seat rest, and means connecting said set of control means to said second set of control means for locking out said second set of control means whereby conflicting signals cannot be transmitted to said motor means.
 6. In an adjustable chair as defined in claim 5 wherein said second set of controls is located on another side edge of said backrest.
 7. In an adjustable chair as defined in claim 4 wherein said set of control means includes a three-position switch for moving said backrest to a reclined position and to an upright position relative to said seat rest; said three-position switch including first means for providing a neutral position, second means for actuating said motor means to recline said backrest relative to said seat rest, and third means for actuating said motor means for moving said back rest to an upright position relative to said seat rest.
 8. In an adjustable chair as defined in claim 7 wherein said third means includes means for holding said switch in position to continually actuate said motor means until said backrest reaches the extreme upright position relative to said seat rest.
 9. In an adjustable chair of the type including a seat rest and a backrest, support means fixedly secured adjacent to a lateral edge of said seat rest and extending upwardly therefrom in a first substantially vertical plane, said backrest including lateral flange portions each integral with a lower portion of said backrest and extending forwardly therefrom in a second substantially vertical plane parallel to said first substantially vertical plane, and pivot means connecting said flange portions to said support means for pivotally mounting said backrest to said seat rest for rotation about a horizontal axis of said pivot means disposed above the plane of said seat rest.
 10. In an adjustable chair as defined in claim 9 wherein means are provided for rotating said backrest to a lowermost position with said backrest being disposed below a horizontal plane passing through a portion of said backrest adjacent to said seat rest.
 11. In a dental chair having a seat rest and a backrest mounted for movement relative to said seat rest, a leg rest, means pivotally connecting said leg Rest to said seat rest, a motor for actuating the pivotal movement of said leg rest, control means located on a side edge of said backrest for controlling said motor to effect pivotal movement of said leg rest, and cushion means disposed over said seat rest and leg rest and extending without interruption from a rearward portion of said seat rest to a lower portion of said leg rest for providing a continuous uninterrupted supporting surface for all positions of said seat rest and said leg rest relative to each other.
 12. An adjustable chair as defined in claim 4 wherein a second set of control means is provided for reclining said backrest relative to said seat rest and for moving said backrest to an upright position relative to said seat rest, said sets of control means being respectively located on opposite side edges of said backrest.
 13. An adjustable chair of the type including a seat rest and a backrest pivotally mounted for movement relative to said seat rest, and motor means for actuating the pivotal movement thereof; said motor means comprising a reversible motor, and a set of control means located on said backrest for reclining said backrest relative to said seat rest and for moving said backrest to an upright position relative to said seat rest, wherein a second set of control means is provided for reclining said backrest relative to said seat rest and for moving said backrest to an upright position relative to said seat rest, and wherein one of said sets of control means is operable for reclining or moving said backrest in the absence of a signal from the other of said sets of control means.
 14. An adjustable chair as defined in claim 6 wherein the second set of control means is operable in the absence of a signal from the other set of control means, and wherein a signal from the other set of control means overrides a signal from the second set of control means.
 15. An adjustable chair as defined in claim 13 wherein said second set of control means is inoperable upon actuation of said other set of control means.
 16. In an adjustable chair as defined in claim 4, further including means for elevating and lowering said chair, wherein said set of control means includes a three-position switch for raising said chair to an elevated position and for lowering said chair to a lower level position; said three-position switch including first means for providing a neutral position, second means for actuating said elevating and lowering means to raise said chair to an elevated position, and third means for actuating said elevating and lowering means for lowering said chair from an elevated position to a lower position.
 17. An adjustable chair of the type including a seat rest and a backrest pivotally mounted for movement relative to said seat rest, and motor means for actuating the pivotal movement thereof; said motor means comprising a reversible motor, and a set of control means located on said backrest for reclining said backrest relative to said seat rest and for moving said backrest to an upright position relative to said seat rest, wherein said control means includes a switch for controlling movement of said backrest toward an upright position by energizing said motor means, and further including means for holding said switch in position to energize said motor means until said backrest reaches an extreme upright position relative to said seat rest.
 18. An adjustable chair as defined in claim 17 wherein said control means includes a second switch for controlling reclining movement of said backrest, and resetting means for deactivating said holding means incident to actuation of said second switch. 